Nano illumination microscopy: a technique based on scanning with an array of individually addressable nanoLEDs

Fluorescence Multi-Detection Device Using a Lensless Matrix Addressable microLED Array

A Point-of-Care system for molecular diagnosis (PoC-MD) is described, combining GaN and CMOS chips. The device is a micro-system for fluorescence measurements, capable of analyzing both intensity and lifetime. It consists of a hybrid micro-structure based on a 32 × 32 matrix addressable GaN microLED array, with square LEDs of 50 µm edge length and 100 µm pitch, with an underneath wire bonded custom chip integrating their drivers and placed face-to-face to an array of 16 × 16 single-photon avalanche diodes (SPADs) CMOS. This approach replaces instrumentation based on lasers, bulky optical components, and discrete electronics with a full hybrid micro-system, enabling measurements on 32 × 32 spots. The reported system is suitable for long lifetime (>10 ns) fluorophores with a limit of detection ~1/4 µM. Proof-of-concept measurements of streptavidin conjugate Qdot™ 605 and Amino PEG Qdot™ 705 are demonstrated, along with the device ability to detect both fluorophores in the same measurement.

Monolithic integrated light-emitting-diode/photodetector sensor for photoactive analyte monitoring: design and simulation

We present the simulation and design optimization of an integrated light-emitting-diode/photodetector (LED-PD) sensor system for monitoring of light absorbance changes developing in analyte-sensitive compounds. The sensor integrates monolithically both components in a single chip, offering advantages such as downsizing, reduced assembly complexity, and lower power consumption. The changes in the optical parameters of the analyte-sensitive ink are detected by monitoring the power transmission from the LED to the PD. Ray tracing and coupled modeling approach (CMA) simulations are employed to investigate the interaction of the emitted light with the ink. In highly absorbing media, CMA predicts more accurate results by considering evanescent waves. Simulations also suggest that an approximately 39% change in optical transmission can be achieved by adjusting the ink-deposited layer thickness and varying the extinction coefficient from 10-4 to 3×10-4.

On-site growth of perovskite nanocrystal arrays for integrated nanodevices

Despite remarkable progress in the development of halide perovskite materials and devices, their integration into nanoscale optoelectronics has been hindered by a lack of control over nanoscale patterning. Owing to their tendency to degrade rapidly, perovskites suffer from chemical incompatibility with conventional lithographic processes. Here, we present an alternative, bottom-up approach for precise and scalable formation of perovskite nanocrystal arrays with deterministic control over size, number, and position. In our approach, localized growth and positioning is guided using topographical templates of controlled surface wettability through which nanoscale forces are engineered to achieve sub-lithographic resolutions. With this technique, we demonstrate deterministic arrays of CsPbBr₃ nanocrystals with tunable dimensions down to <50 nm and positional accuracy <50 nm. Versatile, scalable, and compatible with device integration processes, we then use our technique to demonstrate arrays of nanoscale light-emitting diodes, highlighting the new opportunities that this platform offers for perovskites' integration into on-chip nanodevices.

MicroLED/LED electro-optical integration techniques for non-display applications

MicroLEDs offer an extraordinary combination of high luminance, high energy efficiency, low cost, and long lifetime. These characteristics are highly desirable in various applications, but their usage has, to date, been primarily focused toward next-generation display technologies. Applications of microLEDs in other technologies, such as projector systems, computational imaging, communication systems, or neural stimulation, have been limited. In non-display applications which use microLEDs as light sources, modifications in key electrical and optical characteristics such as external efficiency, output beam shape, modulation bandwidth, light output power, and emission wavelengths are often needed for optimum performance. A number of advanced fabrication and processing techniques have been used to achieve these electro-optical characteristics in microLEDs. In this article, we review the non-display application areas of the microLEDs, the distinct opto-electrical characteristics required for these applications, and techniques that integrate the optical and electrical components on the microLEDs to improve system-level efficacy and performance.

Photon extraction enhancement of praseodymium ions in gallium nitride nanopillars

Lanthanoid-doped Gallium Nitride (GaN) integrated into nanophotonic technologies is a promising candidate for room-temperature quantum photon sources for quantum technology applications. We manufactured praseodymium (Pr)-doped GaN nanopillars of varying size, and showed significantly enhanced room-temperature photon extraction efficiency compared to unstructured Pr-doped GaN. Implanted Pr ions in GaN show two main emission peaks at 650.3 nm and 651.8 nm which are attributed to ³P₀-³F₂ transition in the 4f-shell. The maximum observed enhancement ratio was 23.5 for 200 nm diameter circular pillars, which can be divided into the emitted photon extraction enhancement by a factor of 4.5 and the photon collection enhancement by a factor of 5.2. The enhancement mechanism is explained by the eigenmode resonance inside the nanopillar. Our study provides a pathway for Lanthanoid-doped GaN nano/micro-scale photon emitters and quantum technology applications.

Sub-50 nm control of light at 405 nm with planar Si nanolens

We studied the super-resolution light modulation capability of Si nanodisks, a flat semi-transparent high index nanolens in the visible spectral range. A Laguerre-Gaussian beam-based optimization algorithm was developed to synthesize desired field distributions. Focused spots below 45 nm (< λ/9) were successfully achieved with 405 nm light over the whole center area of the nanolens. This superb light nano-focusing capability allows us to synthesize complex nano-patterns by simply superposing several focus spots together, making the Si nanolens a promising tool for super-resolution photolithography.

Muscope: a miniature on-chip lensless microscope

We report the Muscope, a miniature lensless holographic microscope suitable for on-chip integration. The prototype of the Muscope measured approximately only 7 mm × 4 mm × 4 mm, and was capable of offering a sub-micron half-pitch resolution. We have used, for the first time, a microLED display as the light source in a microscope. The individual pixels of a microLED display chip are used as programmable, microscopic and intense LEDs which can be spatially moved in a two-dimensional plane with a 5 μm pitch. This unique feature set of the display was used to implement computational super-resolution and wide-field imaging without any extra hardware, unlike many other lensless microscopes. We also report a new method to evaluate the magnification in our setting. The Muscope surpasses the existing lensless microscopes in compactness, scalability for production, automated operation and system integration. It provides exciting opportunities for a new class of devices with in-built optical imaging and monitoring and/or sensing capabilities.

A Compact Raster Lensless Microscope Based on a Microdisplay

Lensless microscopy requires the simplest possible configuration, as it uses only a light source, the sample and an image sensor. The smallest practical microscope is demonstrated here. In contrast to standard lensless microscopy, the object is located near the lighting source. Raster optical microscopy is applied by using a single-pixel detector and a microdisplay. Maximum resolution relies on reduced LED size and the position of the sample respect the microdisplay. Contrarily to other sort of digital lensless holographic microscopes, light backpropagation is not required to reconstruct the images of the sample. In a mm-high microscope, resolutions down to 800 nm have been demonstrated even when measuring with detectors as large as 138 μm × 138 μm, with field of view given by the display size. Dedicated technology would shorten measuring time.

Individually Switchable InGaN/GaN Nano-LED Arrays as Highly Resolved Illumination Engines

GaN-based light emitting diodes (LEDs) have been shown to effectively operate down to nanoscale dimensions, which allows further downscaling the chip-based LED display technology from micro- to nanoscale. This brings up the question of what resolution limit of the illumination pattern can be obtained. We show two different approaches to achieve individually switchable nano-LED arrays. We evaluated both designs in terms of near-field spot size and optical crosstalk between neighboring pixels by using finite difference time domain (FDTD) simulations. The numerical results were compared with the performance data from a fabricated nano-LED array. The outcome underlines the influence of geometry of the LED array and materials used in contact lines on the final illumination spot size and shape.

Pursuing the Diffraction Limit with Nano-LED Scanning Transmission Optical Microscopy

Recent research into miniaturized illumination sources has prompted the development of alternative microscopy techniques. Although they are still being explored, emerging nano-light-emitting-diode (nano-LED) technologies show promise in approaching the optical resolution limit in a more feasible manner. This work presents the exploration of their capabilities with two different prototypes. In the first version, a resolution of less than 1 µm was shown thanks to a prototype based on an optically downscaled LED using an LED scanning transmission optical microscopy (STOM) technique. This research demonstrates how this technique can be used to improve STOM images by oversampling the acquisition. The second STOM-based microscope was fabricated with a 200 nm GaN LED. This demonstrates the possibilities for the miniaturization of on-chip-based microscopes.

A Novel Approach for a Chip-Sized Scanning Optical Microscope

The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample with a resolution comparable to the LED sizes, giving rise to chip-sized scanning optical microscopes without mechanical parts or optical accessories. The operation principle and the potential of this new kind of microscope are analyzed through three different implementations of decreasing LED dimensions from 20 µm down to 200 nm.

Optical design of InGaN/GaN nanoLED arrays on a chip: toward: highly resolved illumination

The physical laws of diffraction limit the spatial resolution of optical systems. In contrary to most superresolution microscopy approaches used today, in our novel idea we are aiming to overcome this limit by developing a spatially resolved illumination source based on semiconductor nanoscale light emitting diode (nanoLED) arrays with individual pixel control. We present and discuss the results of optical simulations performed for such nanoLED emitter arrays and analyze the theoretical limits of this approach. As possible designs we study arrays of GaN nanofins and nanorods (obtained by etching nanofin arrays), with InGaN/GaN multi quantum wells embedded as active regions. We find that a suitable choice of the array dimensions leads to a reasonably directed light output and concentration of the optical power in the near field around an activated pixel. As a consequence, the spatial resolution for this type of microscopy should only be limited by the pixel pitch, and no longer by the optical diffraction. Realization of optimized nanoLED arrays has a potential to open new field of chip based superresolution microscopy, making super-high spatial resolution ubiquitously available.